1. Field of the Invention
The present invention relates to a rail guided vehicle system that conveys, along a rail, an article such as a container, in which various kinds of substrates for the production of semiconductor apparatuses, etc., are contained.
2. Description of the Related Art
A conventional rail guided vehicle system is known to be a rail guided vehicle system that conveys an article such as a FOUP (Front Opening Unified Pod) and that includes an overhead hoist transport (so-called OHT) travelling on a rail arranged on a ceiling.
Since such a rail guided vehicle system is often used in a clean room, where the cost of space is expensive, it is necessary to make the rail guided vehicle system smaller. One suggested technique is to make the rail guided vehicle system smaller by shortening the length of a connection rail that connects two main rails. For example, a known technique is to include a forcing guide, configured to force a diverging roller that is used when travelling on the connection rail to shift on the connection rail, in order to shorten the length of the connection rail. See, for example, Japanese Laid-Open Patent Application No. 2008-126743.
Here, the case where the vehicle travelling on a N-shaped rail moves from a rail on which the vehicle is travelling, to another rail is considered as an example. First, the vehicle shifts a diverging roller mechanism to the side on which another rail exists. The diverging roller mechanism is arranged in a travelling unit of the vehicle. Then, the vehicle is guided by a diverging guide, which extends from the rail to the middle of a connection rail, and moves to the connection rail. After this, the diverging roller mechanism is shifted to the opposite side in order for the vehicle to be guided by another diverging guide at the merging side. Here, another diverging guide is arranged in the connection rail and at the position opposite to the diverging guide, with a predetermined offset in between (separating area). In this situation, a forcing guide, which is arranged in the separating area, forces the diverging roller mechanism to be shifted toward another diverging guide. Thus, the travelling unit of the vehicle is guided to another rail.
In the above-mentioned technique, the diverging roller mechanism can only be shifted in the separating area, where the diverging guide does not exist. However, even if the forcing guide is used, the length of the separating area needs to be equal or greater than the length that is derived by adding the length of one diverging roller mechanism along the travelling direction, to the travelling length in which the vehicle travels during shifting the diverging roller mechanism.
For example, in order to shorten the connection rail, it is necessary to shorten the separating area by shortening the length of the forcing guide in the travelling direction. However, when shortening the length of the forcing guide, the diverging roller needs to be shifted rapidly unless the vehicle is slowed down. Shifting the diverging roller rapidly might cause abnormal operation because a large amount of stress is applied to the diverging roller. In addition, since the impulsion generated when the diverging roller abuts the forcing guide is large, the vibration of the vehicle and the damage of the diverging roller may occur.
As described above, the conventional technique has a limited benefit even if the connection rail can be shortened, and the conventional technique has a technical problem of causing various disadvantages when attempting to shorten the connection rail further.